RESUMEN
Benthic exchanges of oxygen and nutrient at the sediment-water interface were investigated under light and dark conditions at 5 selected sites in a sub-tropical atoll. Mean oxygen fluxes were - 1316.5 ± 242.0 µmol m-2 h-1 and mean effluxes of oxygen under light conditions were 2231.7 ± 626.4 µmol m-2 h-1, presumably due to microphytobenthos present at the sediment-water interface. The consequences of this high related productivity was a systematic consumption of nutrients (DIN, PO4 and Si(OH)4) during almost all light incubations, contrasting with the effluxes of nutrients during dark incubations. Our results suggest that the sediments were net autotrophic and the oxygen balance in favor of microbenthic production when compared to community demand. Diurnal rates of gross benthic primary productivity were high (3423 ± 1192 µmol m-2 h-1) which emphasize the role of microphytobenthos in maintaining the oxygen reservoir in tropical lagoons.